This invention relates in general to a heat treating furnace of the type which includes a vessel defining a chamber for holding workpieces, there being heating elements within the chamber to heat the workpieces. More particularly, the invention relates to a furnace in which a quenching gas is circulated through the chamber at the end of the heating cycle for the purpose of cooling the workpieces prior to the workpieces being removed from the chamber.
A furnace of this general type is disclosed in Ipsen U.S. Pat. No. 3,301,541. In that furnace, the vessel is formed by inner and outer spaced apart walls which define a hollow jacket around the heating chamber. During the heating cycle, liquid is circulated through the jacket to keep the outer wall of the vessel cool to the touch. During the cooling cycle, the circulating liquid cools the inner wall of the jacket and also cools the quenching gas within the chamber so as to promote faster cooling of the workpieces.
More than a year prior to the filing date of this application, the assignee of the present invention developed and sold a heat treating furnace which from a structural standpoint, is very similar to that disclosed in the aforementioned Ipsen patent. That is, the furnace which was sold included a vessel having inner and outer walls defining a jacket, heating elements for heating the workpieces in the vessel, and means for circulating a quenching gas within the vessel to cool the workpieces. In that furnace, however, liquid is never circulated through the jacket but instead a vacuum is maintained in the jacket. The vacuum reduces the transmission of heat from the inner wall to the outer wall and thus not only serves to keep the outer wall cool to the touch but also serves to reduce heat losses from the chamber via the walls so as to conserve heat energy.